The present invention relates to a sheet finisher provided with a function by which a sheet delivered from an image forming apparatus such as an electrophotographic copier, printer, facsimile device and a hybrid machine having these many functions is received, stacked in a sheet accommodation section and a finishing such as a folding processing is conducted, and delivered onto a sheet delivery section.
There is provided a sheet finisher by which many number of sheets on which images are recorded by an image forming apparatus main body such as a copier, printer, facsimile device or hybrid machine of these devices are collated for each number of printed volumes, stapled by a stapler and bookbound. This sheet finisher is connected to a print function of the image forming apparatus main body and driven.
As a sheet finisher to conduct the staple processing on a sheet bundle which is a set formed of a plurality of sheets, Japanese Patent Publication Tokkaihei No. 2-276691, 8-319054, or Japanese Patent Publication Tokkohei No. 5-41991 are disclosed.
As the sheet finisher by which a central portion of the sheet bundle is center-stapled, and center-folded at the center-stapled portion and a simple bookbinding is conducted, a sheet finisher written in Japanese Patent Publication Tokkaihei NO. 10-181990 is well known.
This sheet finisher is provided with, for the center-stapling and center-fold processing of the sheet bundle, a center-fold processing section composed of a pair of center-folding rollers which are rotated in pressure-contact with each other, and a center-folding plate to push the center-stapled portion of the sheet bundle in the nip position of the center-folding rollers.
In the sheet finisher to conduct the center-fold processing, there are following problems.
FIG. 18 is a sectional view of the conventional center-fold processing section. The center-fold processing section is structured by a pair of folding rollers composed of an upper roller 83A and lower roller 84A, and a folding plate 82A.
In the center-fold processing section, the center-stapling and center-fold processing, center-fold processing of a small number of sheets, and three-fold processing of a small number of sheets are conducted.
In the case where the center-fold processing is conducted without conducting the staple processing on the small number of sheets, when, while the upper roller 83A and lower roller 84A are rotated, the folding plate 82A is pushed in a nip portion N of the folding roller pair, the sheet S1 in contact with the outer peripheral surface of the upper roller 83A and lower roller 84A reaches the nip position N earlier and is folded, and in a folded portion between it and the sheet S2 in contact with the sheet S1, the slippage between sheets as shown in the drawing, is generated. Particularly, when the advancing speed of the folding plate 82A is lower than the peripheral velocity of the outer peripheral surface of the upper roller 83A and lower roller 84A, the slippage between sheets is conspicuous.
When the advancing speed of the folding plate 82A is made higher than the peripheral velocity of the outer peripheral surface of the upper roller 83A and lower roller 84A, the sheets S1 and S2 which are pushed in by the folding plate 82A are forcibly pushed in the nip position N, and there is a case where a breakage is generated in the sheet bundle.
The object of the present invention is to solve the above problems and to provide a sheet finisher for use with an image forming apparatus by which a good folding processing can be conducted on the sheet bundle.
The above object can be solved by the following sheet finishing method, sheet finisher, and image forming apparatus.
(1) A sheet finishing method in which a sheet delivered from an image forming apparatus main body is conveyed and stacked on a sheet placement table, and the stacked sheets are positioned and aligned, and then folded by a folding means composed of a paired folding rollers and a folding plate, the sheet finishing method is characterized in that it is controlled such that a rotation motion of the paired folding rollers is switched between a state to be rotated along with an advancing motion of the folding plate and a state to be stopped in accordance with the number of sheets stacked on the sheet placement table.
(2) A sheet finisher in which a sheet delivered from an image forming apparatus main body is conveyed and stacked on a sheet placement table, and the stacked sheets are positioned and aligned, and folded by a folding means composed of a paired folding rollers and a folding plate, the sheet finisher is characterized in that it has a detection means for detecting the number of sheets, the first drive means for rotating the paired folding rollers, the second drive means for making the folding plate to advance and retreat, and a control means for controlling the drive of the first drive means and the second drive means, and it is controlled such that a rotation motion of the paired folding rollers is switched between a state to be rotated along with an advancing motion of the folding plate and a state to be stopped in accordance with the number of sheets detected by the detection means.
(3) An image forming apparatus which is characterized in that it is provided with an image forming apparatus main body composed of an image writing means, image forming means, and sheet conveying means and the sheet finisher described in (2).